The invention pertains to uninterruptable power supplies. More particularly, the invention pertains to such supplies that can be used to charge a battery alone or in combination with energizing a DC pump motor.
Uninterruptable power supplies to provide backup in the absence of utility power are known. One such supply is disclosed and claimed in Reichard U.S. Pat. No. 5,508,905, entitled Low Distortion Variable Output Power Supply and assigned to the assignee hereof. The system of Reichard charges a DC battery or batteries, and, in normal operation provides utility supplied AC to a load such as an AC sump pump. In the absence of utility AC Reichard""s system generates an AC output which can be used to energize that pump.
Reichard""s system is AC-to-AC. A market exists for DC sump pumps which are installed to backup a primary AC pump. DC pumps are often small enough that they can be installed into a sump along with a physically larger AC pump. When so installed they provide an additional degree of redundancy.
AC-to-DC backup supplies must address previously unmet challenges. Such supplies store energy in wet cells, for example deep discharge marine batteries. Such batteries must be kept fully charged for long time intervals between utility power failures. When a utility failure occurs, the battery or batteries must be able to immediately start to supply energy to drive the pump.
One known approach to battery charging is to periodically charge the battery or batteries for a predetermined period of time irrespective of their condition. While easy to implement, this approach fails to adequately address fully charged batteries and substantially discharged batteries.
Over-charging is potentially dangerous. Under-charging may result in a battery having inadequate energy in an emergency.
In addition, where a pump is demanding current and the battery or batteries need to be charged, output voltage from the supply can be substantially reduced. Conservation of energy principles require that in such instances, output current from the supply increase significantly and as a result may exceed the ratings of the supply.
Thus there continues to be a need for an uninterruptable power supply for driving DC pumps. Preferably such a supply could not only maintain the battery or batteries in a fully charged condition, without over-charging the battery or batteries, but it will also limit output current so as to protect the integrity of the respective supply. Finally, it would be preferable if such supplies were price competitive with existing supplies.
A high current capacity direct current supply incorporates a programmed processor and executable instructions to monitor changing output load conditions as well as changing utility line input conditions. In one embodiment, energy can be stored in rechargeable, deep discharge marine batteries.
Power conversion in one embodiment can be implemented by one or more transformers in combination with a switching regulator. A variable control signal can be used to vary regulator output. In another embodiment, a transformer can be combined with a linear regulator.
In another aspect, a total output current sensor, coupled to the processor, can be used to monitor output power and to limit maximum output current to a predetermined value. A separate load current sensor, also coupled to the processor, can be used to monitor the load.
Executable instructions, in response to detecting an over current condition, adjust the power conversion circuitry to limit that current. Other instructions maintain charge on the battery or batteries and reduce current thereto so as to avoid an overcharged condition which can damage the battery or batteries.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.